Method for production of isocyanates

ABSTRACT

A PROCESS FOR PRODUCING ISOCYANATES OF THE FORMULA R(NCO)A, WHEREIN R IS A SILYL SUBSITUTED ALKYL, ALKENYL, ALKINYL, ARYL, ALKARYL OR ARALKYL GROUP OR AN ALKYL, ALKENYL, ALKINYL OR ARYL GROUP HAVING NO MORE THAN SIX CARBON ATOMS AND A IS AN INTEGER FROM 1 TO 4, COMPRISING SUBJECTING A SILYL-SUBSITUTED AMINE TO PHOSGENATION AT -80* TO +250*C.

United States Patent 7 Claims ABSTRACT OF THE DISCLOSURE A process ofproducing isocyanates of the formula R(NCO),,, wherein R is a silylsubstituted alkyl, alkenyl,

alkinyl, aryl, alkaryl or aralkyl group or an alkyl, alkenyl, alkinyl oraryl group having no more than six carbon atoms and a is an integer from1 to 4, comprising subjecting a 'silyl-substituted amine to phosgenationat 80 to +250? C.

This invention relates to'methods for the production of isocyanateshaving thegeneral formula R(NCO) wherein R is alkyl, alkenyl, alkinyl,aryl, alkaryl or aralkyl containing elements of the groups IV-VFI of theperiodic system, and alkyl, alkenyl, alkinyl, aryl, alkaryl, or aralkyl,and a is an integer of 1 to 4.

The aforesaid isocyanates find application as components of fuelcompositions and for the synthesis of polyisocyanates, polyurethanes,polyureas and other exten- I sively employed polymers.

Moreover, organometallic diisocyanates, such as organosilicondiisocyanates, may be useful for the productionof appropriatehigh-molecular weight products moditied with isocyanate, urethane, amineand urea groups.

It is known to prepare isocyanates of the above formula by methods (cf.A. A. Blagonravova and G. A. Levkovitch, Uspekhi Khimii, 24, 1955,Moscow) which comprise phosgenating primary amines according to thefollowing reaction scheme:

B01112) COClz R(NC0)1\ 1101 The known methods of preparing isocyanatessuffer from a number of limitations, the major disadvantages being asfollows:

(1) The yield of alkyl and alkenyl isocyanates is low.

(2) The necessity of using a large excess (5- to 7-1fOld excess) ofphosgene which forms with the hydrogen chloride, evolved in the courseof carrying out the reaction, highly aggressive mixtures that do notlend themselves to facile separation and call for the employment of anelaborate system of monitors and eliminators.

(3) Isocyanates are obtained as a mixture with accompanying carbamoyl,chlorides, which in some instances cannot be separated, and with theproducts of isocyanate dimerization or polymerization. 1

(4) The known methods involve several stages for their accomplishmentand call for a strict control of temperature conditions at variousstages. For example, temperature elevation at the last stage of theaforementioned process is conducive, on the one hand, to a higherconversion of the carbamoyl chloride into the sought-for product, but,on the other hand, diminishes markedly the ultimate yield of the targetisocyanate due to its enhanced polymerization, whilst at lowertemperatures the carbamice oyl chloride undergoes but an incompletedecomposition, thereby decreasing the yield of isocyanates.

(5) In some cases, it is mandatory to carry out phosgenation in organicsolvents, which serve the useful purpose of preventing the reactionmixture from being thickened but, at the same time, aifect adversely theefficiency of the process, inasmuch as a large excess of the solventscall for the employment of a more elaborate flow sheet and increasesoperating expenses.

.It is an'object of the present invention to eliminate theaforementioned disadvantages.

The principal object of the present invention is to pro vide a one-stagemethod for the production of isocyanates of the aforesaid generalformula which will make it possible to use the stoichiometric amounts ofthe reactants and to obtain high-purity target products.

This object is accomplished by the provision of a method for theproduction of isocyanates which comprises treating primary amines withphosgene, wherein, according to the invention, silyl-substituted primaryamines are phosgenated at a temperature of from minus 80 to plus 250 'C.

The reaction proceeds in accordance with the following schematicequation:

It follows from the above reaction scheme that the process involves theformation of an intermediate product, viz., N-silyl carbamoyl chloridecontaining a chlorine atom in the [i-position to the silicon atom, whichundergoes spontaneous and irreversible decomposition and yields achlorosilane and the sought-for isocyanate.

To provide for a uniform removal of the heat evolved in the course ofthe exothermic phosgenation reaction and also with a view to depressingthe formation of by-prodnets and, accordingly, increasing the yield ofthe soughtfor products, it is expedient to carry out the process attemperatures below the temperature of phosgene condensation, i.e. in theminus to 0 range.

In order to prevent side reactions and increase the yield of the targetproducts, the phosgenation of silyl-substituted amines at elevatedtemperatures should be carried out in an inert organic solvent medium.

The isocyanates of the aforesaid general formula can be obtained byphosgenating the compounds of the formula R s )2-bla wherein R is alkyl,alkenyl, alkinyl, aryl, alkaryl, or aralkyl containing elements of thegroups IV-VII of the periodic system, alkyl, alkenyl, alkinyl, aryl,alkaryl, and aralkyl;

R is hydrogen, alkyl, aryl, alkaryl, or aralkyl taken singly or invarious combinations thereof;

a is an integer of 1 to 4, and

b is an integer of 0 to 1.

Isocyanates represented by the general formula wherein R, R stand foralkyl or aryl taken singly or in a combination;

R R stand for hydrogen, alkyl, aryl, alkaryl, and aralkyl taken singlyor in various combinations thereof;

Q is a divalent aliphatic or aromatic radical containing elements of thegroups IV-VII of the periodic system and a divalent aliphatic oraromatic radical;

c is an integer of to 1,

can likewise be prepared by phosgenating silyl-substituted primaryamines having the general formula $11 si-cH-oH-(Q).NH-

L pu uv {'{v 9 wherein R", R R, R and Q stand for radicals as definedhereinabove;

c is an integer from 0 to 1, and e is an integer greater than unity.

Isocyanates of the general formula RNCO, wherein R is as defined before,can be prepared by phosgenating silylsubstituted primary aminesrepresented by the formula R, R and R are as defined before, and d is aninteger of 3 or greater.

The present method has made it possible to prepare novel compounds whichare also claimed in the present invention.

The novel compositions of matter-isocyanates are represented by thefollowing general formulae:

wherein R, R R R and Q stand for radicals defined before;

c is an integer of 0 to 1, and

Q is oxygen, sulphur, -(Cl-l wherein 121, and

ortho-, meta-, or para-phenylene The present method for the productionof isocyanates of the general formula R(NCO),, is accomplished in thefollowing manner.

Silyl-substituted primary amines are added, with stirring, to liquidphosgene, the reactants being taken in stoichiometric amounts or thephosgene being taken in a slight excess. The reaction is carried outunder mild conditions in the temperature range of from minus to plus 250C. At elevated temperatures, it is expedient to carry out thephosgenation in an inert organic solvent medium, such as cumene,toluene, and dichlorobenzene.

Upon the termination of the reaction, the reaction mixture is subjectedto fractional distillation to recover the sought-for product. v

For a better understanding of the present invention, the followingexamples of preparing isocyanates are given by way of illustration.

EXAMPLE 1 Methyl isocyanate In a four-necked flask, fitted with a refluxcondenser, a stirrer, a thermometer, and a dropping funnel, there iscondensed 30-35 g. (0.30-0.35 mole) of phosgene and to the contents ofthe flask maintained at a temperature of 35 to 40 C. is added during 1hour 29-34 g. (0.29-0.34 mole) of methylaminotrimethylsilane. Then, thereaction mixture is heated to room temperature and, with a rectifyingcolumn connected to the reaction flask, fractionated to yield 14.9 g. ofmethyl isocyanate (approx. of the theoretical amount) boiling in the43-45 range and 29.8 g. of trimethylchlorosilane (approx. of thetheoretical amount); B.P. 56-57 C.

EXAMPLE 2 Methyl isocyan ate By following the procedure of Example 1,52.5 g. (0.3 mole) of bis-(trimethylsilyl)methylamine and 32 g. (0.32mole) of phosgene are reacted to yield 60 g. of trimethylchlorosilane(94% of the theoretical amount) and 15.4 g. of methyl isocyanate (90% ofthe theoretical amount); B.P. 44-45 C.

EXAMPLE 3 Methyl isocyanate By following the procedure of Example 1, 33g. (0.33 mole) of phosgene is reacted with 32.3 g. (0.33 mole calculatedas monomer) of a mixture of linear, cyclic, olygomeric and polymericsilazanes, prepared by treating dimethylchlorosilane with an excess ofmethyl amine in benzene. Dimethyldichlorosilane is obtained in aquantitative yield (B.P. 6970 C.) and the yield of methyl isocyanateequals 17.1 g. (91% of the theoretical amount); B.P. 43-45 C.

EXAMPLE 4 Isobutyl isocyanate To 15 g. (0.15 mole) of liquid phosgenemaintained at 40 C. there is added, with vigorous stirring, a solutionof 17 g. (0.12 mole) of N-trimethylsilylisobutyl amine in 50 ml. ofcumene. The mixture is heated to 20 C., followed by distilling off theexcess phosgene, removing by filtration a small amount of theprecipitate formed, and fractionating the clear solution thus obtainedwith a Hempel column. The reaction products consist oftrimethylchlorosilane (98% of the theoretical amount) and 10.5 g. ofisobutyl isocyanate (90.5% of the theoretical amount); B.P. 101-102 C.

EXAMPLE 5 Allyl isocyanate In a four-necked flask of Example 1 there iscondensed 30-35 g. (0.30-0.35 mole) of phosgene and to the contents ofthe flask maintained at a temperature of -35 to 40 C. is added for aperiod of one hour 38 g. (0.29

mole) of. N-trimethylsilylisopropyl amine in 100ml. of anhydrous'isopropylbenzene. Then the reaction mixture is brought to boiling andthe excessphosgene is distilled off; The residue is boiled for-2 hourswith a reflux condenser so as to maintain in the flask a temperature of95-98 .C,, followed by fractionating the reaction productswith' a40-cm."column. The reaction yields 22 g. of trimethylchlorosilane (69.3%of the theoretical amount) and 20.5 g. of allyl isocyanate (84% of thetheoretical amount); B.P. 83.5 C. at 740 mm. Hg. 3

By following the procedure disclosed in Example 5, 22.6 g. (0.2 molecalculated as monomer) of a mixture of linear, cyclic, oligomeric andpolymeric N-allyl-methylsilazanes of the type lN Lt... all

wherein d 3 and 21 g. (0.21 mole) of phosgene yield 14.2 g. (87%. of thetheoretical amount) of allyl isocyanate; B.P. 83-85 C.

EXAMPLE 8 a Phenylisocyanate In a four-necked flask of Example 1 thereis condensed 22 g. (0.22 mole) of phosgeneand, while maintaining thetemperature in the flask at 80 to .50 C., 33 g. (0.2 mole) .ofphenylaminotrimethylsilane is added, with stirring, thereto for a periodof 1 hour. Then the reaction mixture is brought to room temperature, asmall quantity of precipitate formed is filtered off, and the filtrateis fractionated to yield 17.4 g. (85% of the theoretical amount) oftrimethylchlorosilane and 19 g. (80% of the theoretical amount) ofphenyl isocyanate; B.P. 162 C.

EXAMPLE 9 Phenyl isocyanate I By following the procedure of Example 8,the reaction between 23.7 g. (0.1 mole) of N-bis(trimethylsilyl) anilineand '11 g. (0.11 mole) of phosgene yields 8.9g. of phenyl isocyanate(75% of the theoretical) and 17.3 g. ofstrimethylchlorosilane (80% ofthe theoretical).

. EXAMPLE 10 Y Phenyl isocyanate In accordance with the procedure ofExample 8, the reaction between g. (0.1.m01e calculated as monomer) of amixture of linear, cyclic, oligomeric and polymericN-phenylmethylsilazanes of the type wherein 423 and 10.5 lg. (ca. 0.1mole) of phosgene yields 9.0 g. of phenyl isocyanate (77% of thetheoretical amount) and 10.3 g. of dimethyldichlorosilane of thetheoretical amount).

EXAMPLE 11 'y-Diethylmethylsilylpropyl isocyanate A mixture of 9.0 g.(0.09 mole) of diethylmethylsilane and 11.4 g. (0.09 mole) ofN-trimethylsilylallyl amine in the presence of 5 drops of the Speierscatalyst on boiling for a period of 2 hours (the ultimate temperature inthe flask is 160 C.) yields 18.8 g. of 'y-(trimethylsilylamino)propyldiethylsilane; B.P. 63 C./ 2 mm. Hg; d 0.8142 and n 1.4405. 1

Into a four-necked flask of Example 1 there is condensed 10 g. (0.1mole) of phosgene while cooling the flask -40-70 C. with a DryIce-acetone mixture, followed b adding to the cooled flask, withvigorous stirring, 16.4 g. (0.07 mole) of'y-(trirnethylsilylaminopropyl) diethylsilane. Then cooling the contentsof the flask isdiscontinued, and the reaction mixture is stirred for 30minutes and thereafter heated to remove the excess phosgene and 5.7 g.(75% of the theoretical) of trimethylchlorosilane. The residue ismaintained for an additional 30 minutes at a temperature of 150 C. andthereafter fractionated in vacuo to yield 8.7 g. of'y-diethylmethylsilylpropyl isocyanate (66.5% of the theoretical); B.P.57-85 C./2 mm. Hg; (1 0.8963; 12 1.4478.

Treating1.2 g. of 'y-diethylmethylsilylpropyl isocyanate with aqueousammonia results in the formation of 1.3 g. ofN-'y-diethylmethylsilylpropyl urea (99% of the theoretical); M.P. 107 C.(recrystallization twice from aqueous acetone).

EXAMPLE 12 'y-Dimethylchlorosilylpropyl isocyanate Into a three-necked 2lit flask fitted with a stirrer, a dropping funnel and a refluxcondenser is charged a solution of 96.6 g. (1.7 moles) of allyl amine in300 ml. of anhydrous diethyl ether followed, while stirring the solutionand cooling the flask with a tap water stream, by the dropwise additionof 79 .4 g. (0.8 mole) of dimethylchlorosilane. The reaction mixture isstirred for an additional 30 minutes at room temperature and thereafterfiltered in a stream of nitrogen. The hydrochloride of allyl amineseparated from the reaction mixture is washed with three 50-ml. portionsof anhydrous diethyl ether. The filtrate is fractionated with a 40-cm.rectifying column to yield 74.4 g. of allylaminodimethylsilane (76% ofthe theoretical); B.P. 99-100 C.; d 0.7704; 11 1.4162. The residue inthe flask consists of N,N-bis (dimethylsilyl) allyl alimine; B.-P. 4546C./15 mm. Hg; d 0.8277; n

Into a two-necked -ml. flask is placed 37 g. (0.3 mole) ofallylaminodimethylsilane, 5-10-drops of a 0.2 N solution ofvH PtCl inisopropanol is added thereinto, and the contentsof the flask arerefluxed until the temperature in the flask rises to 210-220 C. Theresultant viscous, nondistillable polymer is an oily liquid whichdissolves readily in conventional inert organic solvents.

Into a four-necked ZOO-ml. flask, fitted with a condenser and a DryIce-acetone trap, a stirrer, a bubbler, and a thermometer, there iscondensed 35 g. (0.35 mole) of phosgene and, while maintaining atemperature of from -20 to -10 C. in the flask, the polymer dissolved in100 ml. of anhydrous toluene is added dropwise. The reaction mixture isstirred for about 30 minutes at room temperature, then the cold trap isreplaced with a reflux condenser, the excess phosgene is distilled oil,and the solution is refluxed, while being stirred, for a period of 2hours. On stripping ofl' the toluene, the mixture is distilled in vacuumto yield 40.4 g. of y-dimethylchlorosilylproyl isocyanate (71.3% of thetheoretical amount based on monomeric allylaminodimethylsilane); B.P.5253 C./2 mm. Hg and 75-76 C./8 mm. Hg; d 1.0444; 11 1.4528.

7 EXAMPLE 13 1,1,3,3-tetramethyl-1,3-bis ('y-isocyanatopropyl)disiloxane Into a four-necked flask of Example 1 there is condensed 20g. (0.2 mole) of phosgene and to it is added, with vigorous stirring andwhile maintaining the temperature in the flask at -70 to 50 C., for aperiod of 1 hour 42.8 g. (0.2 mole) ofbis-('y-trimethylsilylaminopropyl) tetramethyldisiloxane prepared byhydrosilylation of N-trimethylsilylallyl amine withtetramethyldisiloxane, followed by gradually heating the reactionmixture until it attains room temperature, purging the reaction mixturewith nitrogen, at a slightly elevated temperature, to remove the excessphosgene, and fractionating the residue. The reaction yields 19.4 g. oftrimethylchlorosilane (90% of the theoretical amount), 23.6 g. of1,1,3,3-tetramethyl- 1,3-bis ('y-isocyanatopropyl)disiloxane (70% of thetheoretical amount), B.P. 13l132 C./2 mm. Hg or 115116 C./1.5 mm. Hg, d0.9980, 11 1.4489, and also dimethylchlorosilylpropyl isocyanate (ca.20% of the theoretical amount).

EXAMPLE 14 Bisisocyanatopropyldimethylsilyl)methyl] methane A mixture of6 g. (37.4 millimole) of bis(dimethylsilyl)- methane and 9.7 g. (74.8millimole) of N-trimethylsilylallyl amine is refluxed for 1 hour at atempearture of 110- 190 C. in the presence of the Speiers catalyst toyield 13.0 g. of 'y-(N-trimethylsilylamino)propyldimethylsilylmethane(83% of the theoretical amount), B.P. 148- 150 C./1.5 mm. Hg; d 0.8465;n 1.4565.

Into a four-necked fiask of Example 1 there is condensed approx. g.(0.05 mole) of phosgene and, while maintaining the temperature in theflask at 40 C., to it is added the symmetric disilyl-substituted diamineprepared as described hereinabove. The reaction proceeds rapidly andresults in the formation of a clear solution and an insignificant fineprecipitate. The liquid layer is decanted and freed from the excessphosgene and volatile compounds by heating and purging with nitrogen.The residue is maintained for 1 hour at a temperature of 110-120 C. andthereafter fractionated to yield 7.3 g. ofbis-['y-(isocyanatopropyldimethylsilyl)methyl]methane; B.P. 175- 178C./3.5 mm. Hg; 21 1.4708.

The precipitate is washed with ether, and ether evaporation givesadditional 2.7 g. of the target diisocyanate, the overall yield of thesought-for product being g. (83.3% of the theoretical amount).

EXAMPLE l5 1,2-bis- ('y-isocyanatopropyl) dimethylsilyl] ethane Byfollowing the procedure disclosed in Example 14, the reaction between40.4 g. (0.1 mole) of 1,2-bis[(y-trimethylsilylaminopropyl)dimethylsilyl]ethane and 21 g. (0.21 mole)of phosgene yields 25.4 g. of l,2-biS[('y-is0-cyanatopropyl)dimethylsilyl]ethane; B.P. 134135 C./2 mm. Hg; (1 0.9654;22 1.4715.

EXAMPLE 16 1,3-bis-[ (y-isocyanatopropyl) dimethylsilyl] propane Byfollowing the procedure disclosed in Example 14, the reaction between41.6 g. (0.1 mole) of1,3-bis-[('y-trimethylsilylaminopropyl)dimethylsilyl]propane and 21 g.(0.21 mole) of phosgene yields 28.2 g. of1,3-bis-[('y-isocyanatopropyl)-dimethylsilyl]propane (87% of thetheoretical amount); B.P. 148150 C./2 mm. Hg; (1 0.9591; 1.4701.

EXAMPLE 17 1,4-bis-[ ('y-isocyanatopropyl)dimethylsilyHbenzene Byfollowing the procedure disclosed in Example 14, the reaction between22.6 g. (0.10 mole) of 1,4-bis-[(trimethylsilylaminopropyl)dimethylsilyl]benzene and 21 g. (0.21 mole) ofphosgene yields 31.7 g. of1,4-bis-[('yisocyanatopropyl)dimethylsilyl]benzene (88% of thetheoretical amount); B.P. 180-185 C./2 mm. Hg; d 1.0309; 11 1.5187.

Other mono-, diand polyisocyanates corresponding to the aforesaidgeneral formula can be obtained by following the procedures disclosed inthe examples, the yield being 50% or better of the theoretical.

The present method for the production of isocyanates lends itselfreadily to the employment on a commercial scale and is further noted forits superior efliciency as compared to the prior art methods.

The present method is further advantageous in that it makes possible theproduction of both lower and higher members of isocyanate homologousseries. An added advantage of the present method is that it can beaccomplished at low temperatures, the latter feature being of primeimportance wherein the isocyanates being synthesized the radical Rdefined before contains groupings that are temperature-sensitive in thepresence of phosgene or hydrogen chloride and chlorosilanes formed inthe course of the synthesis of isocyanates.

Such groupings are as follows:

wherein R stands for alkyl, X denotes Hal, N0 or OR, and n is an integergreater than unity.

The present method renders it possible to carry out phosgenation in theabsence of inert organic solvents, thereby making the manufacturingprocess essentially simpler and cheaper.

The present method provides for high yields of the target products notedfor their high purity.

Although the present invention has been described with reference to thepreferred embodiment thereof, it will be readily understood by thoseskilled in the art that various changes or modifications may bepractised therein as long as such changes or modifications mark nomaterial departure from the spirit and scope of the appended claims.

We claim:

1. A method for the production of isocyanates of the formula R(NCO)wherein R is a silyl substituted alkyl, alkenyl, alkinyl, aryl, alkarylor aralkyl group, or an alkyl, alkenyl, alkinyl or aryl groups havingnot more than six carbon atoms, and a is an integer of 1 to 4, whichcomprises subjecting a silyl-substituted amine to phosgenation at atemperature of from minus to plus 250 C.

2. A method according to claim 1, wherein the phosgenation is carriedout at a temperature of from minus 80 to 0 C.

3. A method according to claim 1, wherein thephosgenation is carried outin the presence of an inert organic solvent.

4. A method according to claim 2, wherein the phosgenation is carriedout in the presence of an inert organic solvent.

5. A method according to claim 1, in which the silylsubstituted amine isrepresented by the formula wherein R is as defined above, R is hydrogen,alkyl, aryl, alkaryl, or aralkyl taken either singly or in variouscombinations thereof, a is an integer of 1 to 4, and b is an integer ofto 1, the phosgenation of said compounds yielding isocyanates of thegeneral formula R(NCO),,, wherein R and a are as defined above.

6. A method according to claim 1, in which the silylsubstituted amine isrepresented by the formula wherein R R R R and Q are as defined before,and c is an integer of 0 to 1.

7. A method according to claim 1, in which the silylsubstituted amine isrepresented by the general formula n F l NS1 Ll 1k l wherein R, R, and Rare as defined before, and d is an integer equal to or greater than 3,the phosgenation of said compounds yielding isocyanates of the generalformula RNCO, wherein R is as defined before.

References Cited UNITED STATES PATENTS 3,170,891 2/1965 Speier 260448.2X 3,179,622 4/1965 Haluska 260-448.2 X 3,179,713 4/1965 Brown 260448.2 X3,320,184 5/1967 [Fink 260448.2 X 3,426,057 2/1969 Kanner 260-4482 N3,453,243 7/1969 Hartlein 260-4482 X TOBIAS E. LEVOW, Primary ExaminerP. F. SHAVER, Assistant Examiner U.S. Cl. X.R.

